Adversity, we are told, heightens our senses, imprinting sights and sounds precisely in our memories. But new Weizmann Institute research, which appeared in Nature Neuroscience this week, suggests the exact opposite may be the case: Perceptions learned in an aversive context are not as sharp as those learned in other circumstances. The findings, which hint that this tendency is rooted in our species' evolution, may help to explain how post-traumatic stress syndrome and other anxiety disorders develop in some people.
To investigate learning in unfavorable situations, Dr. Rony Paz of the Institute's Neurobiology Department, together with his student Jennifer Resnik , had volunteers learn that some tones lead to an offensive outcome (e.g. a very bad odor), whereas other tones are followed by pleasant a outcome, or else by nothing. The volunteers were later tested for their perceptual thresholds that is, how well they were able to distinguish either the "bad" or "good" tones from other similar tones.
As expected from previous studies, in the neutral or positive conditions, the volunteers became better with practice at discriminating between tones. But surprisingly, when they found themselves exposed to a negative, possibly disturbing stimulus, their performance worsened.
The differences in learning were really very basic differences in perception. After learning that a stimulus is associated with highly unpleasant experience, the subjects could not distinguish it from other similar stimuli, even though they could do so beforehand, or in normal conditions. In other words, no matter how well they normally learned new things, the subjects receiving the "aversive reinforcement" experienced the two tones as the same.
Paz: "This likely made sense in our evolutionary past: If you've previously heard the sound of a lion attacking, your survival might depend on a similar noise sounding the same to you and pushing the same emot
|Contact: Yivsam Azgad|
Weizmann Institute of Science